1. Field of the Invention
This invention relates to ignition devices or igniters for igniting solid propellant rocket motors, and more particularly, to an improvement that facilitates the development and assembly of inexpensive igniters that are compatible with the rocket motor solid propellants that they are designed to ignite.
2. Description of the Prior Art
In the design and development of igniters for solid propellant rocket motors, the igniter size and characteristic operation, as calculated by the rocket motor engineer, may be a bit off, that is, slightly incorrect. When such an error in calculation occurs, the igniter burn rate may be somewhat incompatible with the ignition characteristics of the rocket motor solid propellant that is intended to be ignited.
Prior art procedures for making corrections for such errors have been expensive and time consuming. It is difficult to change the characteristic behavior of the solid propellant charge used in the igniter as by changing its formulation or geometry. It is also difficult to recalculate and to refabricate the igniter.
In the prior art, ignition of conventional solid propellant rocket motors usually has been by either of two methods. Early rocket motor designs and many smaller motors currently in production use so-called bag igniters including a squib or electric match in the bag with a granular or pelletized first fire agent. One form of such a bag igniter is disclosed in U.S. Pat. No. 3,357,190 granted on Dec. 12, 1967 to H. W. D. Cassidy et al. Such igniters are not well adapted to development and evaluation. Moreover, they have been found to be disadvantageous because of the lack of protection of the deflagrating material contained in the bag from damage tending to result from mechanical shock or exposure to harmful gases in the environment in which the igniters are stored before they are used.
Larger and more recent solid propellant rocket motors have employed as an igniter a miniature rocket motor together with an appropriate first fire device. Igniters of this type are disclosed in U.S. Pat. Nos. 2,897,649 granted Aug. 4, 1959 to R. Reddy and 3,069,843 granted Dec. 25, 1962 to T. S. Whitsell, Jr. This type of igniter has one or more nozzles, is quite complex and expensive to build, and includes reciprocating members that change the nozzle area as a function of chamber pressure or control forces. Such igniter structures consequently also are not well adapted to a development and evaluation situation.
Accordingly, there exists a need in the art of igniting rocket motor solid propellants for an improvement that will facilitate the development and assembly of a simple and inexpensive igniter that is operative without change in a particular solid propellant charge that it is desired to employ, to produce at optimum pressure and burning rate, and to effectively propagate, the high temperature gases that are required for proper ignition of the propellant in the rocket motor in which the igniter is to be used.